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########################################################################
##
## Copyright (C) 2008-2024 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## This file is part of Octave.
##
## Octave is free software: you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING. If not, see
## <https://www.gnu.org/licenses/>.
##
########################################################################
## -*- texinfo -*-
## @deftypefn {} {@var{fjac} =} __fdjac__ (@var{fcn}, @var{x}, @var{fvec}, @var{typicalx}, @var{cdif}, @var{err})
## Undocumented internal function.
## @end deftypefn
function fjac = __fdjac__ (fcn, x, fvec, typicalx, cdif, err = 0)
if (cdif)
err = (max (eps, err)) ^ (1/3);
h = err * max (abs (x), typicalx);
fjac = zeros (length (fvec), numel (x));
for i = 1:numel (x)
x1 = x2 = x;
x1(i) += h(i);
x2(i) -= h(i);
fjac(:,i) = (fcn (x1)(:) - fcn (x2)(:)) / (x1(i) - x2(i));
endfor
else
err = sqrt (max (eps, err));
signp = sign (x);
signp(signp == 0) = 1;
h = err * signp .* max (abs (x), typicalx);
fjac = zeros (length (fvec), numel (x));
for i = 1:numel (x)
x1 = x;
x1(i) += h(i);
fjac(:,i) = (fcn (x1)(:) - fvec) / (x1(i) - x(i));
endfor
endif
endfunction
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